.. as does GR, already long termed 'battle hardened' ..

there was always dissatisfaction with 'dark matter' as an unseen source of gravitational mass .. in a post here some months ago I linked to an article discussing GR as containing the solutions to the 'extra' gravitational energy (ie 'extra' as seen from a Newtonian viewpoint, but apparently not from a GR viewpoint) .. these guys seem to have done the hard grunt and come up with theoretical GR matches for 4 observed galaxies. It seems they are using the GR 'founding principle' that there is no intrinsic difference between accelerations and gravitational forces (the 'equivalence principle') - they are equivalent for all conceivable experiments and obsevers. .. now, any rotation, like circular motion, always involves acceleration - the direction of velocity changes at every moment. So by the equivalence principle the rotation of the galaxy is going to, in effect, 'equal' some kind of 'gravitational field' which then accounts for all (or maybe only part) of the gravitational energy previously attributed to dark matter.

(I say 'in part' as I'm not sure whether, under GR considerations there are other effects as well, for instance that the actual volume 'occupied' by an object like the Sun is greater than we would otherwise expect due to the warping of space inside the Sun itself - caused by the mass itself of the Sun. Maybe this consideration also contributes in some way to 'unseen matter' and its effects .. I don't know)